The National Strong Motion Network
Strong motion seismographs are shoe box sized instruments designed to record the details of very strong ground motions wherethe traditional high-gain seismographs used to routinely locate earthquakes go off scale. They are often called accelerographs because they measure acceleration of the ground. For complete characterization of the ground movement, shaking is measured in three perpendicular directions (one vertical, and two horizontal). Strong motion records of earthquakes are extremely useful to engineers designing earthquake resistant structures.
The Geological Survey of Canada has developed a new type of strong motion seismograph called the Internet Accelerograph which is permanently connected to the Internet and records data continuously rather than in "triggered mode". The new instrument also continuously computes a set of parameters which characterize the intensity of shaking and actively reports those values whenever ground shaking exceeds certain levels to the GSC's data centres. Waveform data can be retrieved from an instrument at any time over the Internet.
Older type accelerographs typically operate in triggered mode. They only begin recording when the ground shaking exceeds a given threshold, typically 0.25 - 1% g, with g being the earth's acceleration. Data retrieval required a visit to the site.
The Geological Survey of Canada operates a network of more than 110 strong motion instruments in the seismically-active area of British Columbia. About 105 of those are the new type of Internet Accelerographs. The majority of these instruments are located in urban settings in the more densely populated southwest corner of the province. The Ministry of Transportation in British Columbia currently has six of its own instruments integrated with the network. In addition, British Columbia Hydro has deployed strong motion instruments at a number of their facilities across the province.
In Eastern Canada the GSC operates a network of eighteen instruments radiating out from the seismically active Charlevoix zone. Hydro-Quebec has installed instruments at four hydro-electric dams to provide free-field and structural response for generating systems along the Manicouagan River. They have also instrumented eight high voltage substations to characterize the response of the the overburden after three stations were severely damaged during the 1988 Saguenay Earthquake. In addition, Gaz Metropolitain has one free field digital accelerograph installed at its LNG plant in Montreal, and New Brunswick Power has one at the Point Lepreau nuclear generating station.
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